Project Summary/Abstract: Pediatric patients in need of thoracic (heart or lung) transplantation suffer unacceptably high mortality on the waitlist, even when there are significant number of donors that go unutilized. Many donors that are determined high-risk and wasted could benefit high-risk recipients that are more likely to die waiting. We propose (Aim 1) development of an innovative risk-based matching of donor and recipient. This will be achieved by developing pediatric specific, donor and recipient risk scoring models for heart and lung transplantation. Risk stratification derived from the scores will then be used in simulation-based models to identify best matching strategy that could deliver optimal overall outcomes for the transplant community (more patients transplanted, shorter waiting time, reduce wait-list mortality and more years of life post-transplant for the community as a whole). Furthermore, pediatric thoracic transplant community is still using an age-old method of weight/height-based donor to recipient size matching which leads to significant number of donors being refused for size mismatch. We also propose (Aim 2) development of in innovative and universally accessible tool for virtual matching of organ size rather than patient size to improve size matching for pediatric thoracic transplantation. This will include development of validated tools for cardiac and lung volume estimation and a clinical study to demonstrate potential benefits of the tool in pediatric heart and lung transplant candidates. Our team has gathered preliminary data to support the premise and feasibility of this project and has the members representing diverse perspective and strengths needed for this project. At the end of this project, we will be able to demonstrate potential benefits of donor- recipient risk matching and organ sizing matching that could improve donor utilization and reduce size mismatch and ultimately improve the impact of pediatric thoracic transplantation.